The present invention relates to a system and method for controlling operation of ultraviolet lamps. More particularly, it relates to a system and method that optimizes lamp life of an ultraviolet air treatment device otherwise operating to reduce or eliminate microorganisms within an air handling system, especially in residential applications.
Though invisible to the naked eye, a multitude of airborne germs (e.g., bacteria, mold spores, etc.) exist, many of which have adverse implications for humans. The likelihood of inhaling or contacting one or more of these germs is elevated in enclosed areas, such as a home, office, etc. In most residential and commercial environments, an air handling system is in place, whereby outdoor air may be drawn into the home or building via a fresh air intake that merges with a return air duct, and then is subjected to heating or cooling conditions (e.g., via a furnace, air conditioner, etc.). As used throughout this specification, the phrase “air handling system” is in reference to a residential or commercial air handling system that has heating and/or cooling capabilities. The heated or cooled air is forced through auxiliary ductwork back to the rooms or offices. Thus, airborne germs entrained in the fresh and/or return airflow are effectively “concentrated” within the air handling system.
A commonly employed technique for eliminating airborne contaminants otherwise permeating through an air handling system is implementation of one or more air filters. While effective in removing a number of unwanted particles, these filters require relatively frequent replacement, and may not be able to consistently remove the smaller particle sized airborne germs. An alternative technique that has proven highly viable is the use of ultraviolet light/energy to kill airborne microorganisms.
In general terms, ultraviolet air treatment devices include one or more appropriately sized ultraviolet lamps that are positioned within the air handling system's ductwork. The ultraviolet lamp is normally mercury-based, with the ultraviolet air treatment device including a power supply ballast used to energize the mercury. For residential applications, the ultraviolet air treatment device is mounted to the outside of a return air duct of the air handling system, with the lamp(s) protruding inside of the duct itself. Alternatively, for other environmental applications, the ultraviolet air treatment device can be mounted to an appropriate duct (e.g., a re-circulation duct associated with a hospital clean room, etc.). Regardless, ultraviolet air treatment systems have proven highly effective in removing a vast majority of the airborne germs commonly encountered. One example of an ultraviolet air treatment device is available under the trade name “Enviracaire Elite UV100E Ultraviolet Air Treatment System” from Honeywell Inc., of Golden Valley, Minn.
Efforts have been made to improve the life and operational characteristics associated with ultraviolet air treatment lamps. For example, non-ozone producing lamps are now available. However, the method of controlling operation of the ultraviolet air treatment device has essentially remained unchanged. In particular, the ultraviolet lamp(s) is simply powered on following installation, and is never shut off. Regardless of whether the air handling system is active or inactive, the ultraviolet lamp(s) stays on twenty-four hours a day. While viable, this approach is quite inefficient in that when the air handling system is inactive, there is virtually no “new” air requiring ultraviolet energy treatment, so that powering of the ultraviolet lamp serves no purpose. As a result, continuous powering of the ultraviolet lamp needlessly consumes a relatively substantial portion of the lamp's useful life, thereby requiring more frequent lamp replacement (and thus increased maintenance costs) and excess energy consumption.
Alternatively, some existing ultraviolet air treatment systems control ultraviolet lamp activation/deactivation based directly upon operation of a fan otherwise associated with the air handling system. For example, most air heating systems including a fan or blower that draws air through the return duct and forces it past a furnace. These alternative control systems make use of the fact that airflows past the ultraviolet lamp only when the fan is operational to power the lamp on when the fan is on, and shut the lamp off when the fan is off. While this technique overcomes the performance issues of other control systems whereby the lamp inefficiently remains on during periods of air handling system inactivity, it does not serve to extend the lamp's useful life. In particular, the life cycle of low pressure mercury-based ultraviolet lamps is dictated not only by cumulative hours of lamp operation, but also by the number of lamp cycles (i.e., number of times the lamp is turned off and on). With this in mind, it has been found that deactivating/activating the ultraviolet lamp with every fan oscillation actually decreases the useful lamp life as the acceptable number of lamp cycles is quickly exceeded. Further, providing a direct electrical connection to the air handling system fan/blower (e.g., fan motor current monitor, sail switch, etc.) entails additional costs, low reliability, and installation complexities, giving rise to other potential limitations.
Ultraviolet air treatment devices continue to be highly popular for removal of airborne germs. In fact, ultraviolet air treatment devices are now becoming prevalent in residential applications. An obvious concern associated with these, and other installations, is cost. Unfortunately, currently available ultraviolet lamp control systems and methods overtly decrease a useful life of the ultraviolet lamp, either by inefficient lamp usage and/or unreasonable lamp cycling. Therefore, a need exists for a system and method for optimally controlling an ultraviolet air treatment device used, for example, to treat air within a return duct of an air handling system.